1. Field of the Invention
The present invention relates to a process for the stabilization of polychlorinated alkanes against dehydrochlorination. More particularly, the present invention relates to the prevention or reduction of dehydrochlorination of 1,1,1,3,3-pentachloropropane when heated in the presence of iron(III) contamination by the addition of monomethyl ether hydroquinone.
2. Brief Description of Art
The Montreal Protocol of 1987 placed a ban on certain substances that deplete the ozone layer, especially chlorofluorocarbons (CFC""s). To hasten the elimination of CFC production and use, the Protocol allowed for certain fluorocarbon products (HCFC""s) to be used as xe2x80x9cbridge replacements.xe2x80x9d Although these bridge replacements are considerably more ozone friendly than CFC""s, they are intended to be transitional and not permanent replacements. Fluorocarbon producers are actively pursuing replacement candidates known as xe2x80x9cthird generation fluorocarbons.xe2x80x9d These third generation fluorocarbons will require hydrochlorocarbon feedstocks.
The second largest U.S. fluorochemical end-use market, next to refrigeration, is for blowing agents utilized in the manufacture of various synthetic plastic formed products. CFC-11 was the dominant product in this market; however, it has been replaced by the bridge-fluorocarbon HCFC-141b. Because current regulations require foam manufacturers to transition away from HCFC-141b by the year 2003, new third generation fluorocarbon products must be developed and commercialized.
Several fluorochemical producers have targeted fluorocarbon 1,1,1,3,3-pentafluoropropane, utilizing 1,1,1,3,3-pentachloropropane (5CP) as the hydrochlorocarbon feedstock, as the primary replacement product for foam blowing applications. The commercial production of 5CP results in a product which is purified through a series of distillation steps. The presence of iron catalyst used in the reaction to produce 5CP, however, allows for the possibility of iron contamination of the product purification section of such a commercial plant. In addition, many non-ferrous alloys actually contain small amounts of iron which can contribute trace quantities of iron to process streams if any corrosion occurs.
Polychlorinated alkanes such as 1,1,1,3,3-pentachloropropane are known to be susceptible to dehydrochlorination in the presence of iron(III). Since iron is or may be present in the process operation steps downstream from the reactor, a need therefore exists to reduce or prevent dehydrochlorination of 5CP in the presence of iron(III).
Various additives are known to be useful to prevent the oxidation and/or polymerization of halogenated compounds such as polychlorinated alkanes in the presence of air or various metals. One such compound, monomethyl ether hydroquinone, also known as MEHQ or p-methoxyphenol, is well known as an additive for halogenated compounds to prevent oxidation and/or polymerization.
Kita et al ( JP Kokai 50088007, xe2x80x9cStabilization of 1,1,1-Trichloro-ethanexe2x80x9d) and Marsden et al (GB 1265567, xe2x80x9cStabilizers for 1,1,1-Trichloro-ethanexe2x80x9d), for example, describe the use of MEHQ to stabilize 1,1,1-trichloroethane against oxidation in the presence of aluminum. Nakatsukasa et al (JP 47011045 B4, xe2x80x9cStabilization of Trichloroethylene or Tetrachloroethylenexe2x80x9d), Campbell et al (DE 2008617, xe2x80x9cStabilized Trichloroethylenexe2x80x9d), and others, describe the use of MEHQ to stabilize trichloroethylene and/or tetrachloroethylene against heat, light, air, humidity, and contact with metals. Numerous authors also disclose the use of MEHQ to inhibit polymerization of vinyl monomers, including vinyl chloride, vinylidene chloride, or other vinyl group-containing monomers (e.g., JP Kokai 48092310 to Oshima et al, xe2x80x9cVapor-Phase Polymerization inhibition of vinylidene chloridexe2x80x9d; DE 2148185 to Fruhwirth et al, xe2x80x9cPolymerization inhibitor for vinyl group-containing aliphatic, aromatic, and heterocyclic compoundsxe2x80x9d; U.S. Pat. No. 3,696,050 to Wert et al, xe2x80x9cPolymerization inhibitors for vinyl monomers and unsaturated polyestersxe2x80x9d; U.S. Pat. No. 3,346,551 to Moakes, xe2x80x9cStabilization of vinylidene chloridexe2x80x9d). However, these documents describe MEHQ as preventing oxidation, hydrolysis, or polymerization; suppression of dehydrochlorination is not mentioned.
Several patents also teach stabilization of fluorinated alkanes with MEHQ. These fluoroalkanes are used in vapor degreasing applications or cleaning of circuit boards. However, MEHQ is used to prevent oxidation, hydrolysis, or polymerization, rather than dehydrochlorination. See, for example, Cook et al (U.S. Pat. No. 4,961,870, xe2x80x9cAzeotrope-like compositions of 1,1,2-trichloro-1,2,2-trifluoro-ethane, 1,2-dichlorethylene, and alkanol having 3 to 7 carbon atomsxe2x80x9d) and Gorski (U.S. Pat. No. 4,804,493, xe2x80x9cStabilized azeotrope or azeotrope-like composition of 1,1,2-trichloro-1,2,2-trifluoroethane and trans-1,2-dichloroethylene for cleaning circuit boardsxe2x80x9d and U.S. Pat. No. 4,803,009 A, xe2x80x9cStabilized azeotrope or azeotrope-like composition of 1, 1,2-trichloro-1,2,2-trifluoroethane, methanol, and 1,2-dichloroethylene for cleaning circuit boardsxe2x80x9d).
Brooks et al (U.S. Pat. No. 5,683,554, xe2x80x9cF141B Crude Stabilizationxe2x80x9d) discloses the addition of various compounds, including MEHQ, to prevent the formation of 1,1-difluoro-1-chloroethane (F142b) when heating 1,1-dichloro-1-fluoroethane (F141b) in a distillation column. In the background disclosure, it is postulated that 142b xe2x80x9cresults from a breakdown of 141b to 1130 (1,1-dichloroethylene) and HF which, in turn, reacts with 141b to produce 142b.xe2x80x9d However, suppression of dehydrochlorination is not mentioned, even though these compounds contain chlorine. Instead, only the formation of F142b, not dehydrohalogenation of 141b, is disclosed.
In view of the susceptibility of polychlorinated alkanes such as 1,1,1,3,3-pentafluoropropane (5CP) to dehydrochlorination in the presence of iron(III), a need therefore continues to exist to provide a process which suppresses the dehydrochlorination of such polychlorinated alkanes.
It is an object of the present invention to provide a process which suppresses the dehydrochlorination of polychlorinated alkanes. The process preferably reduces or prevents the dehydrochlorination of polychlorinated alkanes when heated in the presence of iron(III), or the dehydrochlorination of polychlorinated alkanes under storage conditions. More particularly, in a preferred embodiment, the process reduces or prevents the dehydrochlorination of 1,1,1,3,3-pentachloropropane (5CP) when heated in the presence of iron(III). In another preferred embodiment, the process reduces or prevents the dehydrochlorination of 1,1,1,3,3-pentachloropropane (5CP) under storage conditions.
In accordance with one aspect of the present invention, a process is provided which suppresses the dehydrochlorination of a polychlorinated alkane when heated in the presence of iron(III) by adding an effective amount of a phenol compound to suppress dehydrochlorination. A process is also provided which suppresses the dehydrochlorination of a polychlorinated alkane under storage conditions by adding an effective amount of a phenol compound to suppress dehydrochlorination.
In accordance with another aspect of the invention, the process of the invention provides the addition of an effective amount of a phenol compound which is unsubstituted or substituted in one or more ring positions during the production, manufacture or storage of a polychlorinated alkane to suppress dehydrochlorination due to the presence of iron(III) contamination. Crude polychlorinated alkanes are usually prepared in a reaction vessel using a suitable catalyst system. The catalyst is subsequently removed from the crude product. The product is then sent to one or more fractionating columns for purification. At least two columns will typically be utilized for such product purification. Dehydrochlorination of the desired product due to iron(III) contamination may occur in any or all of the columns utilized in such a process. For this reason, dehydrochlorination stabilization may be necessary in any or all of such columns. The dehydrochlorination stabilizer may therefore be added to any or all of such columns as needed to suppress the dehydrochlorination of the polychlorinated alkane. It may also be added to one or more polychlorinated alkanes, or mixtures thereof, in order to improve the storage stability of the polychlorinated alkane(s).
The process of the invention relates to the addition of an effective amount of a phenol compound to suppress dehydrochlorination of polychlorinated alkanes due to the presence of iron(III) contamination.
In an exemplary embodiment, the process of the invention includes the addition of an effective amount of monomethyl ether hydroquinone (MEHQ) during the production, manufacture or storage of 1,1,1,3,3-pentachloropropane to suppress dehydrochlorination due to the presence of iron(III) contamination. The crude 1,1,1,3,3-pentachloropropane will usually be prepared in a reaction vessel using a suitable catalyst system. The catalyst is removed from the crude product, which is then sent to one or more fractionating columns for purification. The column(s) will preferably be operated at subatmospheric pressure. Typically, at least two columns will be used; the first will remove light ends in an overhead fraction while the pentachloropropane product and heavy ends are removed in the bottoms fraction. The bottoms are then sent to a second column in which purified pentachloropropane product is removed overhead and the heavy ends comprise the tower bottoms. Dehydrochlorination of the desired product due to iron(III) contamination can occur in either or any of the columns, although it is more likely to occur in the bottoms of the second or final tower. A dehydrochlorination stabilizer such as MEHQ can be added to any of the columns as needed.
In a preferred embodiment, MEHQ is utilized as the dehydrochlorination stabilizer and is added to the feed to the first tower. In this way, the MEHQ will effectively inhibit dehydrochlorination in the first tower and will also concentrate in the tower bottoms. It will then pass with the unfinished pentachloropropane product in the bottoms fraction into the second and any subsequent columns, where it will continue to suppress dehydrochlorination of the pentachloropropane.
One process for the manufacture of 1,1,1,3,3-pentachloropropane is disclosed in commonly-assigned copending U.S. application Ser. No. 09/671,993 filed Sept. 29, 2000, the di incorporated herein in its entirety. U.S. Pat. No. 5,902,914, herein incorporated by reference, discloses a process for the preparation of halogenated alkanes including 1,1,1,3,3-pentachloropropane, pentachlorobutane, and heptachlorohexane. U.S. Pat. No. 6,187,978, herein incorporated by reference, further discloses a continuous process for preparing halogenated alkanes using an addition reaction.
By the phrase xe2x80x9csuppress dehydrochlorination,xe2x80x9d it is intended that dehydrochlorination of the polychlorinated alkane when heated in the presence of iron(III), or during storage of the polychlorinated alkane, is preferably reduced or prevented.
The degree of suppression of dehydrochlorination of the polychlorinated alkane due to heating in the presence of iron(III), or during storage of the polychlorinated alkane, may be determined by measuring the effect of the dehydrochlorination stabilizer on the rate of formation of dehydrochlorination by-products present in the polychlorinated alkane product. One such suitable method includes a comparison of the rate of formation of one or more of such dehydrochlorination by-products present in the polychlorinated alkane after it is heated or stored in the presence of iron (III) and in the absence of the dehydrochlorination stabilizer with the rate of formation of the same one or more such dehydrochlorination by-products present in the polychlorinated alkane after it is heated or stored in the presence of iron (III) and the dehydrochlorination stabilizer. In general terms, the degree of dehydrochlorination suppression, i.e. the percentage reduction in the rate of formation of such one or more dehydrochlorination by-products, may be determined for such by-products according to formula (I):                     DDS        =                                            (                                                R                  1                                -                                  R                  2                                            )                                      R              1                                xc3x97          100                                    (        I        )            
wherein,
DDS=degree of dehydrochlorination suppression, in percent;
R1=average rate of formation of the dehydrochlorination by-product upon heating or storage in the absence of the dehydrochlorination stabilizer (excluding the first overhead sample); and
R2=average rate of formation of the dehydrochlorination by-product upon heating or storage in the presence of the dehydrochlorination stabilizer (excluding the first overhead sample).
The suppression of the dehydrochlorination of a polychlorinated alkane when heated in the presence of iron (III) may be determined using the rate of formation of a dehydrochlorination by-product which appears in the overhead product of one or more distillation columns operating at reflux conditions. In one aspect of the invention, the rate of formation of 1,1,3,3-tetrachloropropene (4CPe) expressed in grams/hr may be determined from the amount of 4CPe in the overhead samples and the total time at reflux conditions. An average rate of formation of 4CPe may then be calculated by measuring the amount of 4CPe collected from the overhead over the period of time during which the samples are collected. Since the first sample may contain 4CPe that was present in the initial charge, and may therefore not accurately represent the amount of 4CPe actually formed during the test, it may be excluded from the calculation of the average rate of formation of 4CPe. By calculating the average rate of formation of a dehydrochlorination by-product such as 4CPe which appears in the overhead when a dehydrochlorination stabilizer such as MEHQ is not added, and the average rate of formation of a dehydrochlorination by-product which appears in the overhead when a dehydrochlorination stabilizer is added, the degree of dehydrochlorination suppression (DDS) according to formula (I) may be calculated.
The determination of the degree of dehydrochlorination suppression by the above-described method is based partly upon the assumption that all the dehydrochlorination by-product is recovered in the overhead. In the case of dehydrochlorination stabilization of 5CP, where the rate of formation of 4CPe may be used to determine the effectiveness of a stabilizer such as MEHQ, a low dehydrochlorination rate should reflect an accurate measurement since virtually all of the 4CPe is expected to be present in the column overhead. Where no stabilizer such as MEHQ is added, and high iron concentrations exist, a dehydrochlorination by-product such as 4CPe may also be present in the column and the bottoms. The determination of the rate of formation of a dehydrochlorination by-product according to the above method under these circumstances may therefore be somewhat understated. The degree of dehydrochlorination suppression (DDS) may be calculated using these xe2x80x9cbaselinexe2x80x9d cases to illustrate the improvement in stabilization due to the added dehydrochlorination stabilizer.
In another embodiment of the invention, a dehydrochlorination stabilizer according to the present invention may be added to one or more polychlorinated alkanes, or mixtures thereof, to improve the storage stability of the polychlorinated alkane(s). Typically, long term storage may include the use of metallic or plastic containers, where water may also be present. Under these conditions, organic decomposition products, including, but not limited to, dehydrochlorination products may be formed. By adding one or more stabilizers according to the present invention, the rate of formation of one or more such decomposition or dehydrochlorination products may be suppressed.
Measurement of the storage stability of polychlorinated alkanes, and of the effects of a dehydrochlorination stabilizer according to the present invention, may be performed by accelerated storage stability testing. One such typical procedure includes the use of small test samples of liquid, typically 50-100 ml, placed in sealed glass or plastic bottles at essentially atmospheric pressure. The vapor space above the samples may be purged, e.g., with either air or nitrogen. Baseline tests to establish a control are conducted with pure solvent (polychlorinated alkane) alone. Metallic or plastic coupons representing the material of construction of the intended storage containers are placed in some of the bottles and either partially or wholly immersed in the liquid. Varying amounts of water may also be added. The bottles are placed in a laboratory oven at approximately 45-55xc2x0 C. to accelerate any degradation that may occur at the lower ambient temperatures which a solvent may typically encounter during storage. An oven with a lighted interior may also be used if it is desired to investigate the effect of light on solvent decomposition. Analysis of decomposition products may be performed at regular intervals (typically at 7, 14, 30, 60 and 90 days) by removing samples from the laboratory oven. Typical analyses include, but are not limited to, acidity, chloride, water or metals content. Gas chromatography may also be used to determine the presence of decomposition products, including, but not limited to, dehydrochlorination products.
The degree of dehydrochlorination suppression, expressed as a percentage reduction in the average rate of formation of one or more dehydrochlorination by-products produced when a polychlorinated alkane is heated or stored in the presence of a dehydrochlorination stabilizer, is preferably at least about 5% to about 100%, more preferably at least about 20% to about 100%, and especially preferably at least about 50% to about 100%. It is most preferred that the degree of dehydrochlorination stabilization is at least about 90% to about 100%.
The term xe2x80x9ceffective amountxe2x80x9d as used herein is intended to mean that the amount of the dehydrochlorination stabilizer is sufficient to suppress the dehydrochlorination of the polychlorinated alkane. The term xe2x80x9cstorage conditionsxe2x80x9d is intended to refer to the conditions under which polychlorinated alkanes and solvents are typically stored. Such conditions usually include ambient temperatures and pressures associated with the storage of chemicals in metallic, plastic or other suitable containers.
Under storage conditions, it is preferred that the degree of dehydrochlorination suppression ranges noted above, expressed as a percentage reduction in the average rate of formation of one or more dehydrochlorination by-products produced when a polychlorinated alkane is stored in the presence of a dehydrochlorination stabilizer, are preferably maintained over a time period of at least about 30 days, more preferably at least about 60 days, and especially preferably at least about 90 days. It is most preferred that the degree of dehydrochlorination stabilization ranges noted above are maintained for at least about 6 months.
In a preferred embodiment, the addition of the phenol compound, preferably MEHQ, to suppress dehydrochlorination of the polychlorinated alkane, preferably 5CP, is added at an effective amount from about 1 to about 120 times the soluble iron concentration in the crude product on a weight basis. An MEHQ/iron weight ratio of from about 5 to about 30 times is more preferred. An MEHQ/iron weight ratio of about 5 to about 10 is especially preferred, and a ratio of about 10 most preferred.
The phenol compound may be unsubstituted or substituted at one or more ring positions. The phenol compound is preferably substituted at one or more ring positions with a substituent selected from hydroxy, alkyl or alkoxy groups, more preferably alkoxy groups. Suitable alkyl groups include lower alkyl groups generally having from 1 to 7 carbon atoms, such as methyl, ethyl, isopropyl, butyl and tert-amyl substituents. For example, p-tert-amyl phenol (PTAP) may be one such suitable alkyl-substituted phenol compound. Suitable alkoxy groups include alkoxy groups generally having from 1 to 7 carbon atoms, such as methoxy, ethoxy, isopropoxy and butoxy substituents. An especially preferred phenol compound is p-methoxyphenol, also known as monomethyl ether hydroquinone or MEHQ.
Although the process has been illustrated herein to reduce or prevent dehydrochlorination in pentachloropropane, it may also be employed to suppress dehydrochlorination in other polychlorinated alkanes. Such polychlorinated alkanes may include those having the general formula CxHyClz, where x can range from 2 to about 15, preferably from about 2 to about 8 and more preferably from about 2 to about 6, y can range from 1 to about (2x+1) and z can range from 1 to about (2x+1). Such polychlorinated alkanes may include, but are not limited to, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,1,2,3-pentachloropropane, 1,1,1,3,3-pentachlorobutane, 1,1,1,3-tetrachloropropane, hexachloropropanes, such as 1,1,1,3,3,3-hexachloropropane, 1,1,1,3,3,5-hexachloropentane (or an isomer thereof) and 1,1,1,3,3,5,5,5-octachloropentane (or an isomer thereof).